Calcium carbonate is widely used as fillers or pigments for plastics, paints, inks, sealants, adhesives, papers, rubbers and the like. For example, as for the sealants, sealants are widely used for the purpose of realizing waterproofing and sealing in the fields of construction, automobile production, floor materials and the like. For use in these fields, sealants are often applied to vertical regions, so that it is required for the sealants not to sag down during the process from application to curing but to have high viscosity and high thixotropy.
In order to solve the above-mentioned problem, inventors of the present invention have already proposed a method for producing a precipitated calcium carbonate (Japanese Unexamined Patent Publication JP-A 10-72215), however, in association with further increase in demand, requests for physical properties are getting higher.
For example, in construction of personal houses, demand for siding boards is dramatically increasing. For such siding boards, sealants of low modulus are used in consideration of repetition of drying and wetting, and movement of members. Since the siding boards expand and contract under the influence of temperature and humidity, it is necessary for the sealants to have joint conformability. In order to impart these features, colloidal calcium carbonate has been used heretofore, whereby the modulus after curing is reduced and conformability to the subject of application can be improved to some extent and fine adjustment of viscosity is enabled. However, for further adjusting the viscosity based on reduction in modulus and addition of trace amount, there is a limitation by way of the conventional colloidal calcium carbonate, and hence those having higher fineness and higher dispersibility are desired.
For paints and inks, colloidal calcium carbonate has been traditionally used. As for paints, a warranty period such as 10-year warranty has been presented in recent years, so that paints having higher durability are requested. Also as for inks, there has been a conventional problem that transparency of the ink lowers due to a difference in refractive index between calcium carbonate and ink vehicle, so that it is requested to reduce the conventional blending amount of the colloidal calcium carbonate while maintaining characteristics of the inks.
Also in plastics, wollastonite or needle-shaped calcium carbonate has been used for preventing the strength of a weld line of a shaped article obtained by an injection molding machine from deteriorating, however, both of them have relatively large particle sizes such as several tens microns to 200 microns, which may raise a problem of inducing a decrease in impact strength. With conventional colloidal calcium carbonate, it was difficult to prevent the strength of a weld line portion from deteriorating, and impact strength from decreasing.
Furthermore, in plastisols, vinyl chloride resins are often used in particular for automobile bodies, however, in recent years, consideration has been made to use acrylic resin as alternatives from the environmental aspect. In particular, in acrylic resins, consideration has been made to reduce a film thickness from the view point of reduction of weight as well as from the view point of cost advantage over vinyl chloride resins, and hence fillers capable of imparting higher viscosity even though the amount of addition is small has been demanded. However, conventional colloidal calcium carbonate could not satisfy this demand.
In light of the circumstances as described above, the present invention provides a surface-treated calcium carbonate that has been treated with an organic surface treating agent, a method for producing the same, and a resin composition containing the same, said surface-treated calcium carbonate having joint conformability as well as viscosity/thixotropy imparting effect when used in, for example, curable resins represented by sealants and adhesives; having high luster, excellent anti-sagging property and high strength of a coating film when used in, for example, paints, inks and plastisols; preventing strength of a weld line surface from deteriorating when used in, for examples, plastics, and said surface-treated calcium carbonate also being capable of providing a resin composition having excellent impact strength and reducing weight by decreasing the adding amount into the resin.
As a result of an extensive series of studies for solving the problems as described above, the inventors of the present invention have found that by performing carbonation reaction while adding a specific substance followed by maturation at a specific concentration, a precipitated calcium carbonate having a specific fineness and excellent dispersibility is obtained; and the calcium carbonate surface-treated with a specific amount of an organic surface treating agent has a specific particle size characteristic and improves the adhesion against the subject to be applied and improves the strength of a coating film to be formed, so that the above problems can be solved, and have thus completed the present invention.